In gas phase polymerization processes, a gaseous stream containing one or more monomers is passed through a fluidized bed under reactive conditions in the presence of a catalyst. A polymer product is withdrawn from the reactor, while fresh monomer is introduced to the reactor to react with the catalyst and replace the removed polymerized product. A gas phase fluidized bed reactor can include a reaction zone and a so-called velocity reduction zone. The reaction zone can include a bed of growing polymer particles, formed polymer particles, and a minor amount of catalyst particles fluidized by the continuous flow of gaseous monomer and diluent to remove heat of polymerization through the reaction zone. A portion of the gases within the reactor can be re-circulated via a cycle gas stream. This cycle gas stream can be passed through a heat exchanger, where at least a portion of the heat of polymerization can be removed, and then compressed in a compressor and returned to the reaction zone. Ongoing efforts have been directed to methods of increasing the control of the product morphology of the resin resulting from the polymerization process. Production of polyolefins in fluidized bed processes may suffer if the product particle size distribution has too many small particles, i.e., fines. Fines can buildup in the heat exchanger tubes or other areas of the reactor system, and may contribute to causing a shutdown. Likewise, high amounts of larger particles increase the likelihood of entrainment from the reactor and plugging of the main cycle gas cooler tubes or of the distributor plate. Additionally, as the amount of larger particles and randomly shaped particles increases there could be a tendency for disruptions in the downstream handling of the resin.
There is a need, therefore, for improved methods for controlling the product morphology of polyolefins produced by various catalyst compositions used in such processes.